1. Field of the Invention
The present invention relates to a chromatographic process using a simulated moving bed. More specifically, the invention relates to the chromatographic process of separating a feed stock containing three components that interact with an adsorbent by different degrees of intensity into fractions that are rich in the respective components using a simulated moving bed. The invention particularly relates to the chromatographic process by which the component in the feed stock that interacts moderately with the adsorbent can be recovered in high purity. According to the invention, sucrose can be recovered in high purity from molasses.
2. Description of the Related Art
Liquid chromatography is used extensively in separating operations on an industrial scale. In the simplest version of chromatographic processes, a single bed packed with an adsorbent is alternately supplied with a feed stock and an eluant and the effluent from the bed is fractionated according to its composition. This method provides for the separation of the feed stock into the respective components but, on the other hand, it requires large volume of eluant and the efficiency of bed is low because it is a batch-wise process.
In contrast, a simulated moving bed process permits continuous operation, requires smaller volume of eluant, provides for higher efficiency of bed; and, hence, it is a favored approach in large-scale chromatographic operations.
In chromatography using a simulated moving bed, a feed stock is, in principle, separated into two fractions, one being rich in a component that interacts strongly with an adsorbent packed in the bed and the other being rich in a component that interacts less strongly with the adsorbent. More specifically, two feed ports, one for the feed stock and the other for the eluant, and two withdrawal ports, one for the fraction rich in the strongly interacting component and the other for the fraction rich in the less strongly interacting component, are simultaneously active in the simulated moving bed and, at a given time interval, these feed-withdrawal ports are switched to the corresponding downstream feed-withdrawal ports. Therefore, with the simulated moving bed system of chromatography, a feed stock containing three components, the first that interacts strongly with the adsorbent, the second that interacts moderately and the third that interacts weakly, cannot be fractionated into separate fractions rich in the respective components. One of the three components will be recovered from the simulated moving bed as a mixture with either one of the remaining components. Consider, for example, sugar beet molasses which contains not only sucrose and ash and other non-sugars but also betaine. The order of the intensity of interaction with strongly acidic cation-exchange resins of alkali metal salt forms which are customarily used in chromatographic separation of sucrose from molasses is: betaine&gt;sucrose&gt;ash and other non-sugars. When sugar beet molasses is fractionated by a conventional chromatographic technique using a simulated moving bed, two fractions are obtained, one being rich in sucrose and the other rich in ash and other non-sugars. The betaine is distributed in both fractions. It is therefore impossible to recover sucrose and betaine separately from the sugar beet molasses by a conventional chromatographic process using a simulated moving bed. Furthermore, the betaine distributed in the sucrose-rich fraction lowers the purity of the sucrose in this fraction.